In the field of railway applications, it is known the use of track circuits performing critical safety functions in the monitoring and management of traffic over a railway network. In particular, rail track circuits are primarily used to detect whether a train is present on a track section; they can be also used to detect broken rails within the track section, and/or to transmit signal aspect information through the rails, for example to communicate movement authorities to transiting trains.
To this end, track circuits use electrical signals applied to the rails and a typical track circuit includes a certain number of rails, forming a given track section, which are in electrical series with a signal transmitter and a signal receiver, usually positioned at respective ends of the given track section. The signal transmitter applies a voltage to the rails and a corresponding current signal is detected by the receiver.
Even if at present track circuits perform properly, they are still subject to certain inconvenients and issues. For example, many signals of different type, such as for instance train detection signals or TDs, CAB signals for allowing train speed reduction, et cetera, are output by the transmitter towards the associated receiver or to a transiting train and may travel at the same time over the rails of a track circuit. This makes difficult to properly perform both tuning of the various types of signals to be received, and maintenance of the track circuit as a whole.
In particular, each signal output by a transmitter can be tuned for example in frequency, amplitude, current, phase and the receiver shall be correspondingly tuned to accept and recognize the signal within a range of frequency, amplitude, timing, phase, duty cycle. The various parameters have to be tuned taking into account other variables, such as the length of the tracks, passages of trains, et cetera.
Nowadays tuning is carried out by regulating one signal at a time using traditional metering instruments with the intervention of two or more technicians on the field. After the initial tuning is completed, when all relevant signals are switched-on all together, they usually interfere among each other, especially when the respective carrier frequencies are mutually close; as a consequence, it is possible that further tunings are needed.
Sometimes it is also possible that at the same type on the same track circuit are present two or more signals of the same type, namely a first one correctly relevant for the specific track circuit, and one or more other signals which instead originate from other track circuits. In these cases, a technician performing tuning would not be able to understand that measurements and tuning executed via current state of the art solutions may be affected by a possible error.
Some further issues and distortions reside in the fact that the travelling signals are sensitive to operational and environmental conditions that impact the initial electrical characteristics of the relevant track section.
As a matter of fact, track circuits may not be configured optimally for the actual conditions and require to perform intense maintenance interventions, wherein they are manually re-calibrated by technicians on the field. Clearly, such maintenance interventions are costly, inefficient, and/or time-consuming. Indeed, track circuit configuration and adjustments require lots of time from maintenance forces and temporarily halt the movement of trains, thus resulting in perturbation of the traffic and in substantial financial losses.